The present invention involves a novel process for producing surfactant agglomerates with improved color for use in detergent compositions by admixing a solid bleaching agent. In particular, the surfactant agglomerate produced by the process of the present invention comprises methyl ester sulfonates (MES) as one of the components. The production of alkali metal salts of .alpha.-sulfofatty acid alkyl esters ("ester sulfonates") by sulfonation of fatty acid methyl esters with gaseous SO.sub.3 and subsequent neutralization of the sulfonic acids formed with aqueous alkali metal hydroxides, for example with sodium hydroxide, has been known for some time. The end products of this process, i.e. the alkali metal salts of the corresponding .alpha.-sulfofatty acid alkyl esters, are predominantly used as detergents in washing and cleaning preparations.
However, all hitherto known production processes have remained unsatisfactory either because, although light colored end products suitable for direct use in the detergent industry can be obtained, the yields of the sulfonation step leading to those products are highly unsatisfactory, or because although high sulfonation yields can be obtained, the color instability of the fatty acids or fatty acid esters in the sulfonation step means that dark-colored to brown-black crude products unsuitable for direct use in washing and cleaning preparations are regularly obtained. Accordingly, a sulfonation step taken to high yields normally has to be followed by bleaching of the dark .alpha.-sulfofatty acid derivatives formed in the sulfonation step to obtain light-colored products suitable for use in washing and cleaning systems. Methyl ester sulfonates in particular have been used in many detergent compositions as "natural" surfactants--i.e. surfactants derived from such sources as tallow, coconut and palm. These products, in particular, have been made only while encountering numerous problems, including the major problem that when combining MES with inorganic powders to make MES agglomerates, such MES agglomerates are generally dark to black in color, and therefore contain qualities unsuitable to the consumer for a detergent product.
Another difficulty of hitherto known processes for the production of aqueous ester sulfonates is that, in the course of the production process, the products accumulate in the form of water-containing pastes having high active-substance content. In particular, past attempts to come up with an acceptably colored detergent product comprising MES yielded high viscosity pastes using other systems. However, pastes such as these can no longer be pumped on their own; the high viscosity behavior of ester sulfonate pastes such as these always involves the risk of blockages in apparatus and pipes. Accordingly, there has long been a need to find production processes for such alkali metal salts of a-sulfofatty acid alkyl esters in which the high viscosity of the products obtained is avoided, or lessened in the process.
A third problem often encountered with ester sulfonates and particularly MES comprising detergents, is that addition of hypochlorite or hydrogen peroxide to the acid mixture to solve the color problem (in addition to causing a highly viscous paste) have also tended to cause hydrolysis at the ester in alkaline solution and formation of a disalt too hydrophilic for general dirt/grease detergency use.
Japanese published patent application no. 84-16870 describes a process for the production of alpha-sulfofatty acid ester salts, in which alpha-sulfofatty acid esters formed during the sulfonation step are bleached with H.sub.2 O.sub.2 in the presence of a polycarboxylic acid or one of its salts and subsequently converted by neutralization into the corresponding alpha-sulfofatty acid esters salt. Although the salts formed are very suitable for use as detergents in washing and cleaning preparations, the reaction time required for the bleaching step is of the order of 1 hour which does not include the time required for the following neutralization reaction.
U.S. Pat. No. 4,547,318 describes a process for the production of color-stable, light-colored aqueous salt pastes of washing-active alpha-sulfofatty acid esters in which the dark-colored alpha-sulfofatty acid esters emanating from the sulfonation step are first prebleached with alkali metal hypochlorites in neutral to mildly alkaline aqueous solution and are then fully bleached with hydrogen peroxide in the usual way in a mildly acidic aqueous solution. The bleaching process as a whole takes several hours, involves a change in the pH value of the reaction medium with all the ensuing disadvantages, and gives aqueous salt pastes of which the active substance content is in the range of from 20 to 60% by weight which, as described above, gives rise to problems affecting the process due to the considerable increase in viscosity with increasing active substance content.
U.S. Pat. No. 3,142,691 describes the production of light-colored sulfonated fatty acids and fatty acid derivatives, more particularly through a process for bleaching dark-colored sulfonated fatty acids and sulfonated fatty acid derivatives by treatment with oxyacids having a strong oxidizing effect, or salts or anhydrides of these oxyacids.
U.S. Pat. No. 4,874,552 describes the production of solid, substantially anhydrous alkali metal salts of alpha-sulfofatty acid alkyl esters by simultaneously mixing the esters with an aqueous solution of hydrogen peroxide or an H.sub.2 O.sub.2 -yielding compound with a solid alkali metal carbonate at particular temperature ranges, optionally in the presence of aqueous alkali metal hydroxide.
The present invention seeks to provide a process for improving the color of surfactant agglomerates, particularly MES comprising agglomerates. It further seeks to provide a process which avoids the prior art two-step process of bleaching and agglomeration separately, with no visible detriment to agglomerate color with time. The present invention further describes a process which avoids the addition of water or aqueous bleaching agents or solutions comprising other bleaching agents, thus reducing the problems associated with high viscous pastes and/or foaming acid product which is often associated with the high quantity of water in the processes of the prior art. In accomplishing this, the present invention seeks to provide the advantage of a process for producing highly active particle agglomerates with decreased water content, which thereby reduces the need for drying of the agglomerates.